1. Field of the Invention
The invention relates to the isolation and mutation of bacterial strains that produce L-lactic acid. The invention also relates to the isolation and mutation of Lactobacillus strains for the production of L-lactic acid, fermentation media and procedures for producing L-lactic acid.
2. Related Art
Lactic acid, CH3CH(OH)CO2H, possesses one chiral carbon and thus can be present in the L- or D-stereoisomeric form. L-Lactic acid (also known as (S)-(+)-lactic acid) in optical purity does not contain any of its enatiomeric pair, D-lactic acid (or, (R)-(−)-lactic acid). As discussed throughout the description, L-lactic acid is interchangeable with S-lactic acid or (+)-lactic acid; D-lactic acid is interchangeable with R-lactic acid or (−)-lactic acid.
Optically pure L-lactic acid has several important industrial applications. U.S. Pat. No. 5,801,025 indicates that L-lactic acid has found its application in various fields including food and pharmaceuticals, brewing, tanning and optical materials. The pesticidal toxin produced by the bacteria of the present invention has attracted attention because it, unlike conventionally used agricultural chemicals, is harmless to humans and animals. U.S. Pat. No. 5,801,025 has also revealed that optically pure L-lactic acid is useful as liquid crystals, and is the preferred stereoisomeric form to be fed to infants.
U.S. Pat. No. 6,229,046 also describes that lactic acid currently used in food applications has chiral purity requirements greater than 95% chiral purity, generally with a preference for the “L” form. The chiral purity of lactic acid is also important for end products such as pharmaceuticals and other medical devices where lactic acid is a starting material.
U.S. Pat. No. 5,801,025 also describes the need for optically pure lactic acid when used as the starting material in the production of polylactic acid, a biodegradable substitute for other polymeric plastics. For example, the higher the optical purity of the starting lactic acid, the higher the degree of crystallization of the polymer produced. The polylactic acid with a high degree of crystallization is suitably used for stretched films and fibers.
U.S. Pat. No. 6,229,046 also indicates that the chiral purity of the lactic acid has a strong influence on the properties of the polymer. U.S. Pat. No. 5,484,881 describes how the crystallinity of polymers of lactic acid requires relatively long sequences of a particular stereoisomer, either long sequences of (R) or of (S) form. The length of the interrupting sequences may be important for establishing other features of the polymer, such as the rate at which it crystallizes, the melting point of the crystalline phase, or melt processability. Further discussion of the importance of optically pure lactic acid or its industrial use can be found, for example, in U.S. Pat. Nos. 5,142,023; 5,338,822; 5,536,807; and 5,585,191.
Lactic acid is widely recognized to be useful as a starting material for producing polylactic acid, a biodegradable plastic that has both environmental and medical advantages. Biodegradable polymers of lactic acid are less harmful to the environment than non-biodegradable polymers in that they more readily decompose. Such biodegradable polymers have also been useful in various medical applications. For example, sutures made of fibers of lactic acid polymers can be bioabsorbed by patients undergoing surgery. Processes of preparing lactic acid and polymers thereof can be found, for example, in U.S. Pat. Nos. 1,995,970; 2,362,511; 2,683,136; 3,636,956; 3,797,499; 5,801,025; 5,142,023; 5,247,058; 5,258,488; 5,357,035; 5,338,822; 5,446,123; 5,539,081; 5,525,706; 5,475,080; 5,359,026; 5,484,881; 5,585,191; 5,536,807; 5,247,059; 5,274,073; 5,510,526; 5,594,095; 5,763,513 and 6,290,896; all of which are herein incorporated by reference.
Methods of producing lactic acid via fermentation processes are described in U.S. Pat. Nos. 4,521,434; 4,839,281; 4,885,247; 4,963,486; 5,147,668; 5,210,296; 5,219,597; 5,234,826; 5,250,182; 5,296,221; 5,324,515; 5,338,682; 5,378,458; 5,416,020; 5,464,760; 5,482,723; 5,503,750; 5,547,692; 5,798,237; 5,801,025; 5,814,498; 5,849,565; 6,187,951; 6,229,046; 6,280,985 and 6,319,382; all of which are incorporated by reference.
The present invention improves upon these methods by providing lactic acid producing bacteria useful in fermentation processes whereby higher yields and greater optical purity of L-lactic acid are achieved. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the invention as claimed.